Introduction

Why is it important to know the energy content of pet foods? Because if the energy content of the food(s) and the quantity of food(s) consumed is known, it is possible to determine how much energy a pet is being fed. This in turn will enable the clinician to provide more precise feeding recommendations to an owner, advice which is particularly important for clients who are in the process of changing their pet’s diet or are feeding multiple diets. Owners may not appreciate that feeding guides can vary between pet food manufacturers, and that different manufacturers may have different approaches to estimating a food’s energy content.

Knowing the energy content of a pet food also means that different diets can be accurately compared. By normalizing to a fixed energy content it is possible to compare nutrient content, or other factors such as cost, across a range of quite different foods, e.g., one can accurately evaluate the difference between a wet and a dry diet. Some pet food manufacturers provide information on the energy content of their diets, but mandatory legislation varies from country to country and there is no standard method as to how the energy content should be calculated. The approach outlined in Table 1 provides a consistent way to estimate the energy content across a range of foods for both dogs and cats.

Foods differ in the amount of energy they contain, and this is primarily a function of the amount of moisture, protein, fat and carbohydrate present, and (in the case of the macronutrients) their respective digestibilities. Typically dry foods are more energy-dense per unit weight than wet foods; the energy content of wet foods can vary from 70-130 kcal/100 g of food, compared with dry foods that can vary from 280-480 kcal /100 g of food.

Measurement of metabolizable energy (ME) content of pet food

The gold standard for measuring ME is to perform a feeding (digestibility) study, but this is time-consuming and expensive to conduct, and many pet food manufacturers do not have the capability or resources to conduct such studies. Predictive equations are an alternative method to feeding studies and can provide a good estimate of a diet’s ME content. There are a number of different predictive equations, but they all use a similar approach based on the amount of protein, fat and carbohydrate in the food, and employ coefficients (and in some cases other factors) to adjust for the digestibility of the food. 

Interpreting nutritional information on pet food labels

Some, but not all, of this information may be provided on the pet food label. It is important to check that nutrient values are expressed in % units, or g/100g of food. It is also essential to verify that the given values represent typical or average values for the nutrient in question; sometimes different values (such as guaranteed minimum or maximum levels) are declared and these should not be used. If it is not clear on the label as to what the values refer to, it is advisable to check with the manufacturer.

The following nutritional values must be known to use a predictive equation; as noted above, values must be expressed as percentages or as g/100g. Also note that the carbohydrate (“Nitrogen Free Extract” or NFE) fraction may not be measured directly but can be calculated by difference (Table 2).

• Moisture
• Protein
• Fat
• Carbohydrate* (NFE)
• Ash **
• Crude Fiber

*if not provided this can be calculated from the other nutrients.
** sometimes referred to as “inorganic matter”.

Key: GE = gross energy - DE = digestible energy - ME = metabolizable energy - CF = crude fiber
- NFE = nitrogen free extract

Royal Canin is pleased to announce the launch of an app that will assist calculation of the estimated metabolizable energy density of dog or cat food from its approximate analysis. Download the app using the relevant link below.